Nicholas Leontyev was a worldly 17-years-old when his mom finally broached the subject of the birds and the bees.

“I just burst out laughing, ‘It’s too late for me, mother!’” he recalled with a chuckle.

In fact, it was four years too late for the sex talk, since the now 29-year-old lost his virginity at the tender age of 13.

Leontyev vowed not to wait that long with his own twin girls.

“I’ll probably have the talk with my kids as soon as I see that they’re lucid and becoming self aware,” the Upper West Side dad said.

He’s hardly alone.

According to a recent Harris Poll, Americans — on average — say kids should get “the talk” at age 12.3. That’s about a year earlier than their parents talked about sex with them, according to the survey.

The Harris Poll asked both adults and teenagers when kids should be able to do a slew of activities for the first time — including wearing makeup, going on their first date and having their first sleepover.

On average, Americans felt that kids are ready for the responsibility of a pet at age 8.9, and they should start receiving an allowance at 9.8.

Sleepovers could start at 10.7, poll respondents said. While first kisses should happen at 15.1 — about a year before it’s appropriate for teens to go on their first date.

Sharon Greer — who has an 11-year-old daughter, Amalia, and a 5-year-old son, Aiden — said she’s fine with her oldest child having sleepovers — as long as they’re at her house.

“Ami has sleepovers now, I know all of her friends and their mothers so it’s okay,” the 32-year-old told The Post. “They’re just little girls, it’s innocent.”

Then Amalia chimed in: “Except she only lets my friends sleep at our house, I can’t sleep at theirs.”

Both mom and daughter began chuckling.

Amy Hanies, of Lancaster, Penn., has a similar strategy, and admitted she doesn’t like to let her 15-year-old daughter Tatum Swift spend the night at pals’ places.

“I never really let her go to sleepovers,” she said. “I allow them to come here, to our home. I am overly protective, and if I don’t know the families, then I don’t know the brothers or siblings. I’m very protective.”

Her daughter said she got so used to it that when she finally did sleep over at someone’s house, she wanted to leave.

Leontyev said he’d defer to his wife on the makeup issue, but agreed his daughters should wait until they’re around 15 to start wearing it.

“I don’t think any father would want his girls getting stared at as if they were women by perverts,” he explained.

Americans said kids should get their first cell phone at age 14, according to the poll. But most New Yorkers interviewed were much younger when they earned that privilege.

“Fourteen is an okay age for a first phone but there are young kids with tablets who have access to the Internet as young as eight or nine years old, completely unrestricted,” said Preston Klepeis, a 28-year-old substitute teacher and parent.

“Parents now didn’t have the same things kids do so they don’t understand the implications.”

Steinberg said that poll respondents who are currently parents were more likely to say kids should have cell phones at a younger age.

‘I consider girls to be adults at the age of 14 and boys to be adults at the age of 28’

- Mom Ellen McHugh

“When you are a parent and you have to know where your kid is and be able to reach them, then the age is a little bit lower,” she explained.

Ninety-percent of Harris Poll respondents insisted that kids today are growing up too quickly — and some New York parents say phones are part of the problem.

“Well, kids know more these days because they’re exposed to more,” Greer said. “On TV, on the Internet, on their cell phones. So in that sense they move faster.”

But she added that every generation seems to think the next one is growing up too quickly.

“I believe every generation perceives the next as moving too fast or growing up too quickly,” she explained.

“But I had my first [child] in my early 20s and now I’m seeing less and less girls having kids that young, so in another sense they’re not moving any faster than we did.”

Ellen McHugh, who lives in Brooklyn with her three boys and works in education, said kids just grow up faster in the Big Apple.

“Kids in New York grow up faster and spend a lot of time with helicopter parents,” she said.

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According to the Harris Poll, kids shouldn’t be considered adults until they’re 18.8.

Klepeis mused that he’d never really see his daughter as one.

“She’ll always be my baby girl,” he said. “Maybe when she has her own children and her own horrible worries in life.”

McHugh had a different take.

“Honestly, I consider girls to be adults at the age of 14 and boys to be adults at the age of 28,” she said.